Direct Thermal Receivers Using Near Blackbody Configurations

Figure 1. Schematic of the cylinder acting as a near-blackbody receiver when solar radiation enters the cylinder's left end

Technology Marketing Summary

Current oil and salt based heat transfer fluids have significant limitations such as usable temperature, high cost, and limited thermal conversion efficiency. To achieve the Department of Energy SunShot goal of high efficiency, low cost renewable power generation, a highly efficient and economical way to absorb solar heat and to store the thermal energy is important for broad deployment of concentrating solar power (CSP) plants as baseload power.

Description

Engineers at the National Renewable Energy Laboratory (NREL) have developed a high-temperature “direct” supercritical CO2 (s-CO2) receiver for CSP applications. The direct s-CO2 receiver can be coupled with an s-CO2-Brayton power cycle to meet the DOE SunShot cost and performance goals. The near-blackbody (NBB) design employs a working mechanism resembling a blackbody furnace, and minimizes thermal losses from convection and radiation through reducing direct exposure of heated surfaces to the cool ambient surroundings. An ideal blackbody furnace design uses a well-known radiative mechanism and captures nearly all incoming radiation. The infrared (IR) re-radiation losses also behave as NBB emission, therefore a significant design emphasis is on minimizing IR emission. The NBB design maximizes solar energy collection efficiency while reducing IR re-radiation and convection losses for high performance.

This receiver design performs at greater than 650°C operating temperature with less than 10% thermal loss (defined as the ratio of energy delivered to the heat transfer fluid divided by the total energy that enters the receiver aperture), while minimizing the thermal stress (and hence material requirements) of the receiver. Such a design enables use in a modular, small tower s-CO2 power system, where the s-CO2 power block may be directly integrated with the receiver on top of the tower, resulting in less piping requirements and parasitic consumptions.